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Flatcar Prototype: Turnbuckles

By mounting the queenposts the waggon’s substructre is now ready for the turnbuckles. The prototype is used to adjust the trusses’ tension in order to avoid the waggon’s floor to sag. I decided to go for a scratch-build again, since the cast pieces are currently very hard to come by and on top of that they would have been the weakest link in my current construction. However, as a matter of fact it’s very time-consuming to build them manually.

First off I purchased some brass pipe with 3 mm outer diameter, but only 1 mm inner diameter. Which is necesarry to construct working threads. From this pipe I cut off pieces of 2 cm length.

First a piece of pipe is cut to length.
First a piece of pipe is cut to length.

Thoses pieces are clamped in a mini drill and chamfered with a key file at the ends.

The ends are chafed.
The ends are chafed.

Next, the inner diameter is widened for the thread bore. I’ve already described how tedious the search for the trusses material turned out to be, but in the end I’ve found steel wire with 1.6 mm diameter. So for the female thread the diameter has to be widened to 1.3 mm.

The inner diameter is widened to the thread hole.
The inner diameter is widened to the thread hole.

At the first try I cut the thread at the very end, but that caused the turnbuckle to warp. To avoid that, it’s preferrable to cut the threads right after widening the diameter, namely a right-hand thread at one end and a left-hand thread at the other one. Thus the turnbuckle can actually adjust the trusses’ tension.

The thread is tapped.
The thread is tapped.

After that it’s time to bring the typical shape of the turnbuckles to light. The middle part’s flanks are milled until two rather slim webs remain.

The flanks are milled into shape.
The flanks are milled into shape.

The gap in the middle needs to be widened to 1.3 mm. To that end, I drill a series of holes with a suitable drill bit…

The flanks are predrilled in the centre.
The flanks are predrilled in the centre.

…and then connect those with a slim milling head.

The centre is reamed.
The centre is reamed.

Naturally, doing that step by hand won’t deliver a smooth result. So the turnbuckle is cleaned out afterwards using a key file. That wouldn’t be necesarry with a proper milling machine, but I lack the pocket change…

The centre is smoothed with a file.
The centre is smoothed with a file.

This includes to file the turnbuckle’s ends as thin as possible. The prototype has got very short threads, which I couldn’t replicate in the model for the brass would give too easily. So I elongated the threads and reduced the outer diameter as far as practicable to conceal them.

The turnbuckles are filed down to their final shape.
The turnbuckles are filed down to their final shape.

Now it’s time to lay the freshly painted waggon on its back and cut the trusses in the middle. A piece of wire has to be removed so the turnbuckle’s gap remains clear.

The trusses are cut in half.
The trusses are cut in half.

As soon as the male threads are tapped, the turnbuckle can be slid on and fastened tight.

The turnbuckle is mounted to the truss.
The turnbuckle is mounted to the truss.

It’s really astonishing how well the turnbuckles perform in the model. The tension can be adjusted very precisely and the long threads absorbe the force very well. This concludes an important building step and I can now focus on other details. Next time, I’m going to focus on the footsteps.

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